The runways, the seal seats, the sill or the lintel of a sluice, in a hydroelectric work, are used to receive a gate or stop logs in order to block and seal the opening in a dam. Its structures are prone to wear as time passes and thus requiring restoration works in order to preserve their functionalities. The traditional underwater structure restoration methods are based on minor repair tasks that may be completed under water by experimented divers and also on major works that require the preliminary installation of a cofferdam in order to dry the work area.
The automated underwater restoration exhibits economical advantages, but raises serious technical problems due to the design of the submersible systems comprising various electromechanical parts. Other problems arise to both ensure automated and remotely operated tasks in an underwater environment, where the human presence is considered dangerous, where the visibility is reduced and the availability of the required sensors is limited. The underwater environment is also a source of important perturbations that may affect the operation of the sensors, the manipulators and other actuators. The control of the machining process is also affected by the underwater environment and poses precision and repetitiveness problems. Furthermore, it is necessary for certain works to perform the restoration in different time windows having variable durations. To optimize the restoration time and allow respecting these time windows, the installation and uninstallation time in the work area must be as short as possible, which implies that it is important to reduce the amount and volume of the equipment to be installed to its minimum, as well as to simplify the complexity of the installation and the number of steps to be followed.
Some apparatuses allowing performing works under water have already been proposed.
For example, U.S. Pat. No. 6,309,147 (Matsumoto et al.) shows a remotely operated tool for drilling a plate in a nuclear reactor vessel. The tool has a drill bit moving along its rotation axis inside a stationary sleeve. The tool is mounted over the plate to be drilled, and a system is provided for collecting the chips resulting from the drilling. The drilling requires that the tool be still and properly fixed with respect to the plate to be drilled, and thus has no lateral or transverse mobility for its displacement, nor vertical other than that relative to the drill bit as required for the drilling. Furthermore, the tool is only provided with a basic controller limited to the operation of the motors of the tool and not designed to have automation capabilities for the drilling task, and even less for other tasks.
U.S. Pat. No. 6,555,779 (Obana et al.) proposes an apparatus that prevents water from entering in a bell covering and sliding on a workpiece, for example for welding or cutting. The apparatus has a pressurized water or gas injection system intended to form a water or gas curtain around the periphery of the bell to prevent water from entering. The apparatus is especially designed for performing a welding task along a line and can be mounted on a track by means of an assembly subjected to no important stresses and having a consequent construction. The control of the welding task is achieved by remote control operations from a worker, or by an automated mechanism reacting to image data captured with a camera during the welding.
U.S. Pat. No. 5,377,238 (Gebelin et al.) proposes a device for cutting or grinding a support of a nuclear reactor fuel assembly. The configuration of the device is specifically adapted to the prismatic geometry of the fuel assembly, and thus has a platform horizontally fastening to a support of the fuel assembly, a mobile carriage mounted on the platform, a hoist for hoisting the assembly, clamping elements for immobilizing the assembly, a table mounted on the carriage with a return element, a tool support mounted on the table, and a tool secured to the tool support.
JP application 2005297090 (Sato et al.) proposes a device for underwater polishing of a workpiece and collecting chips without however requiring a suction pump. The device comprises impellers disposed on the rotation shaft of the tool located in a bell so as to produce a negative pressure in the bell for draining the chips and water towards a filter that collects the chips. The construction of the device only allows light polishing or grinding works
In general, the prior art apparatuses and devices have automation, mobility, portability, installation, robustness, stiffness, precision and/or adaptation capabilities limited to such an extent that they are not adapted to the automation and achievement of intensive machining or measurement works under water, as for the milling of embedded parts of hydroelectric structures. This case of milling involves important stresses and vibrations at the level of the manipulator of the milling tool and requires a good global stiffness.